MHD wrote:Commonly with Sci-Fi you have to go "FTL, Causality, Relativity; choose two."
I like axing causality in my settings.
It's usually more "FTL, Causality, Relativity, Consistency; Choose three".
Take something like Star Trek. They've obviously heard of relativity. There's no time dilation or anything like that, but the light speed still has a special place. They make a big deal of breaking it, and it requires special 'magical' engines. So relativity is there, in some rudimentary form. It's just that they chose to ignore its consequences. So it's consistency they sacrifice.
Most SF with FTL is similar. They don't abandon causality, because that would make a bad story, and they still pay lip service to relativity (All talk about the light speed as being an important barrier, many have some form of time dilation included, etc). So they include all three of the concepts. They just choose to completely ignore the glaring contradictions this causes. This works very well, because most readers aren't aware of them, and those who are generally don't mind too much as long as it's not made too obvious.
Ender's Game for example has relativistic travel combined with instant communication. Noone uses this to send signals back in time, the possibility is never exploited, never even discussed. It's just entirely ignored. The story still works.
It's really only hard SF authors that worry about consistency. Which is why writing hard SF that includes FTL is so ... hard.